Magnetically sensed temperature control device



Dec. 13, 1966 s. LEGVOLD 3,292,124

MAGNETICALLY SENSED TEMPERATURE CONTROL DEVICE Filed Sept. 24, 1964 2 Lu 2 O 2 9 F UJ 2 O z o g a 2 k a 1' TEMPERATURE CURIE POINT OF PURE GADOLINIUM INV ENTO R: SA M LEG VOL D flwmww wa w dawm ATT'YS United States Patent 3,292,124 MAGNETICALLY SENSED TEMPERATURE CONTROL DEVICE Sam Legvold, Ames, Iowa, assignor to Iowa State University Research Foundation, Inc., Ames, Iowa, a corporation of Iowa Filed Sept. 24, 1964, Ser. No. 398,970 2 Claims. (Cl. 335205) The invention described herein was made or conceived in the course of or under a contract with the United States Atomic Energy Commission.

This invention relates to a thermostat, and, more particularly, to a thermostat wherein the sensing element is para-magnetic such as an element containing gadolinium.

Gadolinium is one of the rare earths (atomic No. 64, atomic weight 156.9). This invention is based in part on the fact that gadolinium has a Curie point of about 72 F. Below this temperature, i.e., the Curie point, gadolinium is ferr c-magnetic; above this temperature it is paramagnetic, i.e., only Weakly magnetic.

It is, therefore, an object of the invention to provide a novel thermostat embodying closable contact arms wherein one of the arms is equipped with a gadoliniumcontaining element so as to provide control of a space in the vicinity of the temperatures normally encountered in living areas.

Other objects and advantages of the invention may be seen in the details of construction and operation set down in this specification.

The invention is explained in conjunction with an illustrative embodiment in the accompanying drawing in which:

FIG. 1 is a fragmentary perspective view of a thermostat embodying teachings of the invention; and

FIG. 2 is a graph of the relationship of magnetic moment to temperature for gadolinium.

In the illustration given, and with particular reference to FIG. 1, the numeral 10 designates generally a frame which supports temperature-sensing means and which may be suitably encased for mounting in a space whose term perature is being controlled. The frame 10 carries a first upstanding arm generally designated 11, which may be advantageously constructed of an electrical insulator, i.e., plastic. The arm 11 includes a first upstanding portion 12 and a second upstanding portion 13, developing with the interposed block 14, a general U shape.

The first upstanding portion 12 of the arm 11 is equipped with an electrical contact 15 coupled by means of a wire 16 to means (not shown) for changing the temperature in the space surrounding the thermostat. This may be a heater, furnace, air conditioner, etc.

The second upstanding part 13 is equipped with a ferromagnetic element such as the permanent magnet designated 17 which is adapted to coact with a second element 18 which is constructed, at least in part, of a para-magnetic material such as gadolinium. Other materials may be employed in certain instances such as copper-nickel alloys.

The second contact 18 is carried by the second arm 19, which also advantageously is constructed of an electrical insulator. Further carried by the arm 19 in alignment with the contact 15 is a coacting contact 20 which also is coupled by means of a wire 21 to the above-mentioned heater, air conditioner, or the like.

Providing the support on the frame 10 for the second arm 19 is a coil spring 22 which is carried by a standard 23 upstanding from the frame or base 10. The degree of force required to uncoil the spring 22 is advantageously regulated by means of a screw 24 coupled to the spring 22 and threadedly received within the standard 23. The standard 23 also provides an integral bracket 25 carrying a setscrew 21 which regulates the amount of movement of the second arm 19.

When the gadolinium-containing element 18 is constructed of substantially pure gadolinium, the Curie point thereof is 72 F.--as indicated in the chart of FIG. 2. Consideration of FIG. 2 reveals that the magnetic moment (which may be defined as ergs per oersted) rises rapidly as the temperature decreases in approaching 72 F. At 75 F., for example, there is virtually no magnetic character in the element 18. By the time 65 F. is reached, the magnetic character is greatly increased.

In operation, as the temperature decreases to the Curie point range, greater and greater magnetic attraction exists between the elements 17 and 18, tending to move the contacts 15 and 20 into electrical-conducting contact. When this occurs, the means for controlling the temperature of the surrounding space is energized, or de-energized, as the case may be. By preloading the arm 19as by more tightly coiling the spring 22 the temperature of contact can be reduced below 72 F. as desired.

If temperatures of thermostat operation are desired that are above the curie point of pure gadolinium, the same can be achieved by alloying the gadolinium with carbon, which tends to raise the Curie point, i.e., shifting the point to the right in the showing of FIG. 2.

Other complexing or alloying materials useful in this connection are scandium (atomic No. 21, atomic weight 45.10), lanthanum (atomic No. 57, atomic weight 138.92), lutecium (atomic No. 71, atomic weight 174.99) and yttrium (atomic No. 39, atomic weight 173.04)all of which may be employed for lowering the Curie point of the paramagnetic material, i.e., gadolinium.

While in the foregoing specification a detailed description of an embodiment of the invention has been set down for the purpose of explanation, many variations in the details herein given may be made by those skilled in the art without departing from the spirit and scope of the invention.

I claim:

1. A thermostat, comprising a frame, a pair of contact arms on said frame, means coupled to said arms when the same are in contact for controlling the temperature of the space surrounding said arms, one of said arms being equipped with a ferromagnetic element and the other arm being equipped with a gadolinium-containing element aligned with the first-mentioned element for selective contact therewith, said gadolinium-containing element also containing a member selected from the group consisting of scandium, lanthanum, lutecium, and yttrium, thereby the Curie point of said gadolinium-containing element is lowered below 72 F.

2. A thermostat, comprising a frame, a pair of contact arms on said frame, means coupled to said arms when the same are in contact for controlling the temperature of the space surrounding said arms, one of said arms being equipped with a ferromagnetic element and the other arm being equipped with a gadolinium-containing element aligned with the first-mentioned element for selective contact therewith, said gadolinium-containing element also containing carbon whereby the Curie point of said gadolinium-containing element is elevated above 72 F.

OTHER REFERENCES Metals Handbook, volume 1, 8th ed., p. 1230.

BERNARD A. GILHEANY, Primary Examiner.

R. N. ENVALL, IR., Assistant Examiner. 

2. A THERMOSTAT, COMPRISING A FRAME, A PAIR OF CONTACT ARMS ON SAID FRAME, MEANS COUPLED TO SAID ARMS WHEN THE SAME ARE IN CONTACT FOR CONTROLLING THE TEMPERATURE OF THE SPACE SURROUNDING SAID ARMS, ONE OF SAID ARMS BEING EQUIPPED WITH A FERROMAGNETIC ELEMENT AND THE OTHER ARM BEING EQUIPPED WITH A GADOLINIUM-CONTAINING ELEMENT ALIGNED WITH THE FIRST-MENTIONED ELEMNT FOR SELECTIVE CONTACT THEREWITH, SAID GADOLINIUM-CONTAINING ELEMENTS ALSO CONTAINING CARBON WHEREBY THE CURIE POINT OF SAID GADOLINIUM-CONTAINING ELEMENT IS ELEVATED ABOVE 72*F. 